The present invention relates to a downhole drop ball sub for use in a wellbore. The present invention is highly suitable for use in a downhole surge pressure reduction system or for other purposes. More particularly the present invention relates to a drop ball sub that may be used in conjunction with a running tool or other wellbore tools to allow launching a ball in the wellbore whose diameter is larger than the internal diameter of the running tool, drill string, tubing string, or any other restrictions found in the wellbore. The embodiment of the system for surge pressure reduction also includes a unique enlarged flow path that permits increased flow to reduce surge pressure and better handle debris.
One problem frequently encountered in many wellbore operations is the need to overcome the limitation of a restriction in the wellbore that prevents use of a ball below that restriction where the ball has a diameter greater than the restriction. More particularly, one of skill in the art will realize that it has heretofore been impossible to use a ball downhole that has a diameter which is greater than the diameter of the restriction in the wellbore. The term xe2x80x9cballxe2x80x9d also includes any other suitable object, e.g. bars, darts, plugs, and the like. Typically a ball is used downhole to activate, seal, or otherwise perform a useful function.
One embodiment or use of the present invention is effective for reducing surge pressure. For a long time prior to the previous invention for reducing surge pressure as taught in U.S. Pat. No. 5,960,881, which is incorporated herein by reference, the oil industry had been aware of the problem created when lowering a first casing string, which may be a casing liner, at a relatively rapid speed in drilling fluid. This rapid lowering of the casing liner results in a corresponding increase or surge in the pressure generated by the drilling fluid due to the relatively small annulus between the casing liner and the surface casing. The formation about the borehole into which the casing liner is lowered is exposed to the surge pressure.
This surge pressure has been problematic to the oil industry in that it has many detrimental effects. Some of these detrimental effects are 1.) loss volume of drilling fluid, which presently costs $40 to $400 a barrel depending on its mixture, that is primarily lost into the earth formation about the borehole, 2.) resultant weakening and/or fracturing of the formation when this surge pressure in the borehole exceeds the formation fracture pressure, particularly in older formations and/or permeable (e.g. sand) formations, 3.) loss of cement to the formation during the cementing of the casing liner in the borehole due to the weakened and, possibly, fractured formations resulting from the surge pressure of the formation, and 4.) differential sticking of the drill string or casing liner being run into a formation during oil operations, that is, when the surge pressure in the borehole is higher than the formation fracture pressure, the loss of drilling fluid to the formation allows the drill string or casing liner to be pushed against the permeable formation downhole and allows it to become stuck to the permeable formation.
This surge pressure problem had been further exacerbated when running tight clearance casing liners or other apparatus in the existing casing. For example, the clearances in recent casing liner runs have been about xc2xdxe2x80x3 to xc2xcxe2x80x3 in the annulus between the casing liner and existing casing. This small annulus area in these tight clearance casing liner runs have resulted in corresponding higher surge pressures and heightened concerns over their resulting detrimental effects of surge pressure. The most common known response to surge pressures was to decrease the running speed of the drill string supporting the casing liner downhole to maintain the surge pressure at an acceptable level. An acceptable level would be a level at least where the drilling fluid pressure, including the surge pressure, is less than the formation fracture pressure to minimize the above detrimental effects. Any reduction of surge pressure would be beneficial because the more surge pressure is reduced, the faster the drill string or casing liner could be run. Time is money, and the system of U.S. Pat. No. 5,960,881 significantly reduces the number of hours required for running the casing string downhole while still avoiding the detrimental effects discussed above.
However, it would be desirable to provide an even larger flow path to further reduce surge pressure, to allow better debris removal, and to reduce the possibility of plugging the float equipment. In the prior art, running tools have an internal diameter that is limited or restricted to about 3 inches to 3.4 inches. It would be desirable to use a ball in the wellbore having an outer diameter larger than the restriction of the running tool to actuate, for example, a larger valve in the casing liner float collar or shoe below the running tool. Preferably, it would be desirable to be able to use balls at least in the range of 3xc2xd or 4xc2xd inches in outer diameter. However, it would be expensive to redesign the subsea/liner running tools to have a diameter through which such larger drop ball may pass and such redesign could reduce the tensile strength and hence the holding capability of the running tool.
The present invention allows existing systems for running casing liners to use balls having an outer diameter larger than the internal diameter of existing running tools or any other restriction in the running string. Therefore, the need to pay the high cost of redesigning the running tools is avoided while the advantages of using larger drop balls is achieved. The present invention also provides a larger diameter flow path for returns.
More particularly, the present invention provides a means for launching balls having a larger outer diameter than restrictions in the wellbore that can be used to perform useful functions in the wellbore below the restriction.
A drop ball system is provided for use in a wellbore having a restriction therein with a restriction internal diameter. The drop ball system allows launching a ball whose diameter is larger than the restriction such that the large ball may be utilized below the restriction in the wellbore. The drop ball system may be used with any tool requiring downhole ball activation or where downhole ball activation is desirable. Such applications include but are not limited to use with float equipment, flapper valves, squeeze tools, inflatable packers, running tools, adaptors, and test tools, for zone isolation, squeeze tools, squeeze production, and the like. In one embodiment, the drop ball system may comprise a drop ball housing that is mounted within the wellbore at a position in the wellbore below the restriction. A first ball or large ball is mounted in the drop ball housing which has an outer diameter larger than the restriction internal diameter.
A release element, such as a yieldable seat for the large ball, is provided for supporting the large ball prior to releasing the large ball from the drop ball housing into the wellbore. A second ball or release ball is provided having an outer diameter smaller than the restriction internal diameter. Upon receipt of the release ball in a seat in the housing, the large ball may be released through the release element by increasing the pressure above the release ball. In one preferred embodiment, the release element is a yieldable or breakable seat for the large ball. A moveable member, such as a sliding sleeve, may be mounted in the drop ball housing for engagement with the large ball to apply force to the large ball so as to release the large ball from the drop ball housing.
In one aspect of the invention, a tubing connector is provided on the drop ball housing for mounting the drop ball housing within the wellbore on a tubular element such as onto a string of wellbore tubulars or a continuous wellbore tubular such as coiled tubing. In another aspect of the invention, a wiper plug connector is provided on the drop ball housing so that the drop ball mechanism may be installed in a wiper plug. Thus, it is contemplated that the drop ball housing could be mounted on many different downhole members including members that may also be released into the wellbore. In one aspect of the invention, the drop ball housing consists of drillable material such that the drop ball housing can be drilled out with a wellbore drill bit.
A method is provided for a drop ball system for use in a wellbore having a wellbore restriction with a restriction inner diameter. The wellbore restriction could be one of many types and in many places such as found in tubular strings, running tools, particular tools, and the like. The method includes the step of providing a drop ball housing within the wellbore at a position in said wellbore below the restriction. A first ball or large ball is provided in the drop ball housing having an outer diameter larger than the restriction inner diameter. The large ball is released from the drop ball housing. The drop ball housing may preferably be mounted to a downhole member. The downhole member could be a tubular string, coiled tubing, a wiper plug, or another downhole tool or member. A second ball or release ball is dropped into the wellbore to initiate the step of releasing the large ball. In one embodiment, the drop ball housing is responsive to fluid pressure acting thereon for releasing the large ball.
Thus, the present invention also provides a drop ball system that may be used in a tubular string for running a casing liner: into a wellbore through another casing, such as but not limited to, a surface casing. The tubular string may have at least one restriction in internal diameter located therein. In this case, the restriction is typically in the running tool. A body for a drop ball sub may be provided with a flow path therein. A connector on the body may be used for connecting the drop ball sub to the tubular string at a position in the tubular string below the restriction. A first ball or large ball is mounted within the body. The large ball an outer diameter larger than the restriction internal diameter. A first seat or large ball seat may be provided within the body for the large ball. A second seat or release ball seat may be mounted in the body along the flow path. The release ball seat may be sized for receiving a release ball with an outer diameter smaller than the restriction internal diameter. A moveable sleeve may be connected to the release ball seat for movement in response to fluid pressure acting on the release ball when seated in the release ball seat. The moveable sleeve is preferably moveable from a first position to a second position to thereby cause the large ball to drop out of the body. In a preferred embodiment, the moveable sleeve acts to produce a force on the large ball when the sleeve is moved to the second position.
The system preferably also comprises a first diverter tool mounted in the tubular string on one side of the restriction such as above a running tool. A second diverter tool may be mounted on an opposite side of the restriction such as below the running tool.
Thus, a drop ball sub is described that may be used downhole in a tubular string. The drop ball sub is preferably used for launching the large ball from the drop ball sub in response to dropping the release ball into the drop ball sub through the tubular string. The large ball is larger in diameter than the release ball. The drop ball sub preferably comprises a body defining a passageway for fluid flow through the body. A large ball seat and a release ball seat are mounted in the body along the passageway. The large ball seat is sized to receive the large ball and the release ball seat is sized to receive the release ball. An actuating element may be responsive to receipt of the release ball into the release ball seat in the body for launching the large ball. The actuating element may preferably be a sleeve or slidable element secured to the release ball seat. The actuating element is moveable in response to pressure applied to the release ball seat when the release ball is dropped into the release ball seat. The actuating element may include engagement surfaces for engaging the large ball to thereby launch the large ball.
As a system for improved fluid flow while running a casing liner into a wellbore through a surface casing, the system then comprises a tubular string and a running tool mounted in the tubular string for running a casing liner into the wellbore through the surface casing. A first diverter tool may be mounted in the tubular string above the running tool. A second diverter tool may be mounted in the tubular string below the running tool. The first diverter tool has an open position to permit fluid flow out of the tubular string into the annulus between tubular string and the surface casing, while the second diverter tool has an open position to permit flow of the fluid in the annulus between a cement stinger and the casing liner being run into the tubular string through the running tool. The first diverter tool and the second diverter tool are responsive to a drop ball to move each of them to a closed position to shut off annular fluid flow. The system includes a drop ball sub that may be mounted to the tubular string or a stinger below the running tool. The drop ball sub comprises a large ball with an outer diameter larger than an inner diameter of the running tool. The system preferably includes a valve operable in response to receiving the large ball.
In operation, a method for using a drop ball sub within a tubular string used in a wellbore wherein the tubular string has a restriction with an internal diameter comprises positioning the drop ball sub within the tubular string at a position in the tubular string the restriction. A large ball is provided in the drop ball sub. The large ball has an outer diameter greater than the internal diameter of the restriction. A release ball, which has an outer diameter smaller than the restriction, may be dropped through the tubular string to activate the drop ball sub for dropping the first ball from the drop ball sub. A release ball seat for the release ball is provided in the drop ball sub. The release ball seat is responsive to pressure acting on the release ball seat for launching the large ball from the drop ball sub. A first diverter sub is provided in the tubular string at a position in the tubular string above the restriction. A second diverter sub is provided in the tubular string at a position in the tubular string below the restriction.
An object of the present invention is to permit launching a ball below a restriction in the wellbore even though the ball is larger in diameter than the restriction.
Another object of the present invention is to provide a drop ball sub that permits launching a large ball in response to dropping a smaller ball.
Another object of the present invention is to provide a drop ball sub that may be used with a wide variety of running tools, adaptors, wiper plugs, and the like.
Another object of the present invention is to provide a drillable drop ball sub for use where the drop ball sub may remain downhole and needs to be drilled out by the wellbore drilling bit.
An object of the present invention is to provide a system for increasing flow capacity while running casing and reduce the risk of plugging therein due to debris.
Another object of the present invention is to provide a system for dropping a ball larger than the internal diameter of a restriction in the running string such as the running tool.
Yet another object of the present invention is to provide an additional diverter in the running string so that flow goes into the running string, through the running tool, and back out from the running string into the annulus between the running and the previous string or strings of casing.
These and other objects, features, and advantages of the present invention will be made apparent to those of skill in the art in the following claims, description, and drawings. However, the present invention is not to be limited by any listed objects, features, or advantages that are listed simply as an aid those reviewing the specification to quickly discover some of the many benefits provided by the present invention.